1. Field of the Invention
The invention relates generally to systems and methods for selectively isolating, or closing of a portion of a wellbore.
2. Description of the Related Art
During operation of a hydrocarbon production well, it is sometimes necessary to close off, or “kill,” the well below a certain point, against fluid flow. If the well remains live while, for example, a pump is being removed, pressurized fluid could be forced to the surface very quickly, resulting in a dangerous situation at the wellhead and potentially reducing the ability of the well to produce further. One technique is to kill the well by introducing fluids, such as seawater, at the surface of the well to increase the hydrostatic pressure within the well to a point where it is higher than the formation pressure. The problem with this technique is that it is usually undesirable to introduce fluids into the formation below, as such may reduce the quality and quantity of production fluid that may be obtained from the well later.
A second method for isolating the well is to provide a shut-off valve below the pump that is being removed and then to close the shut-off valve as the pump is removed from the well. A conventional shut-off valve arrangement is a sliding sleeve valve having lateral fluid openings with an internal sleeve that is axially moveable between positions that open and close against fluid communication. A sliding sleeve cut-off valve of this type is described in, for example, U.S. Pat. No. 5,156,220 issued to Forehand et al. and U.S. Pat. No. 5,316,084 issued to Murray et al. Each of these patents are owned by the assignee of the present invention and are hereby incorporated by reference. A shut-off valve assembly of this type is also available commercially from the Baker Oil Tools division of Baker Hughes Incorporated as the Model “CMQ-22” Sliding Sleeve.
This procedure for opening and closing the shut-off valve, while simple, presents practical problems. Because the well is live, there is typically a significant pressure differential across the shut-off valve. The inventors have recognized that, if the valve is not positively closed at the time the pump is removed, pressure may escape from the well below the pump. With the procedure where the sleeve element is closed by pulling the pump from the well, the valve is not fully closed until the pump is raised some distance within the wellbore, thereby permitting such an escape of pressure.
The present invention addresses the problems of the prior art.